The infrared spectrum covers a range of wavelengths longer than the visible wavelengths but shorter than microwave wavelengths. Visible wavelengths are generally regarded as between 0.4 and 0.75 micrometers. The near infrared wavelengths extend from 0.75 micrometers to 10 micrometers. The far infrared wavelengths cover the range from approximately 10 micrometers to 1 millimeter. The function of infrared detectors is to respond to energy of a wavelength within some particular portion of the infrared region.
Heated objects will dissipate thermal energy having characteristic wavelengths within the infrared spectrum. Different levels of thermal energy, corresponding to different sources of heat, are characterized by the emission of signals within different portions of the infrared frequency spectrum. No single detector is uniformly efficient over the entire infrared frequency spectrum. Thus, detectors are selected in accordance with their sensitivity in the range of interest to the designer. Similarly, electronic circuitry that receives and processes the signals from the infrared detector must also be selected in view of the intended detection function.
A variety of different types of infrared detectors have been proposed in the art since the first crude infrared detector was constructed in the early 1800's. Virtually all contemporary infrared detectors are solid state devices constructed of materials that respond to infrared frequency energy in one of several ways. Thermal detectors respond to infrared frequency energy by absorbing that energy causing an increase in temperature of the detecting material. The increased temperate in turn causes some other property of the material, such as resistivity, to change. By measuring this change the infrared radiation is measured.
Photo-type detectors (e.g., photoconductive and photovoltaic detectors) absorb the infrared frequency energy directly into the electronic structure of the material, inducing an electronic transition which, in turn, leads to either a change in the electrical conductivity (photoconductors) or to the generation of an output voltage across the terminals of the detector (photovoltaic detectors). The precise change that is effected is a function of various factors including the particular detector material selected, the doping density of that material and the detector area.
By the late 1800's, infrared detectors had been developed that could detect the heat from an animal at one quarter of a mile. The introduction of focusing lenses constructed of materials transparent to infrared frequency energy, as well as advances in semiconductor materials and highly sensitive electronic circuitry have advanced the performance of contemporary infrared detectors close to the ideal photon limit.
Current infrared detection systems incorporate arrays of large numbers of discrete, highly sensitive detector elements, the outputs of which are connected to sophisticated processing circuity. By rapidly analyzing the pattern and sequence of detector element excitation, the processing circuitry can identify and monitor sources of infrared radiation. Though the theoretical performance of such systems is satisfactory for many applications, it is difficult to actually construct structures that mate a million or more detector elements and associated circuitry in a reliable and practical manner. Consequently, practical applications for contemporary infrared detection systems have necessitated that further advances be made in areas such as miniaturization of the detector array and accompanying circuity, minimization of noise intermixed with the electrical signal generated by the detector elements, and improvements in the reliability and economical production of the detector array and accompanying circuitry.
A contemporary subarray of detectors may, for example, contain 256 detectors on a side, or a total of 65,536 detectors, the size of each square detector being approximately 0.0035 inches on a side, with 0.0005 inches spacing between detectors. The total width of such a subarray would therefore be 1.024 inches on a side. Thus, interconnection of such a subarray to processing circuitry requires a connective module with sufficient circuitry to connect each of the 65,536 detectors to processing circuity within a square a little more than one inch on a side. The subarrays may, in turn, be joined to form an array that includes 25 million detectors or more. Considerable difficulties are presented in aligning the detector elements with conductors on the connecting module and in isolating adjacent conductors in such a dense environment.
Because of their small size and brittle nature, subarrays of detectors are typically mounted upon a substrate so as to facilitate their handling and attachment to multi-layer ceramic modules, which typically contain filter, amplification, and multiplexing circuitry.
one example of a detector interface device or substrate for attaching infrared detectors to multi-layer modules is disclosed in U.S. Pat. No. 4,792,672 issued to SCHMITZ on Dec. 20, 1988 and entitled DETECTOR BUFFER BOARD, the contents of which are hereby incorporated by reference.
The SCHMITZ buffer board does not utilize wings or tabs which serve as handles for facilitating handling and alignment of the substrate with the multi-layer modules. Such tabs, according to the present invention, are preferably configured to have snap-off notches such that the tabs may be broken away from that portion of the substrate upon which the infrared detectors are mounted as discussed in detail below. Thus, the tabs may be utilized to facilitate attachment of the detector interface device, including the infrared detectors attached thereto, to a multi-layer module. The tabs are subsequently removed to facilitate the assembly of a number of such multi-layer modules into a detector array.
Difficulties have been encountered in providing a means for testing the functionality and reliability of individual detector elements after they have been attached to the substrate, as well as after attachment of the substrate to a multi-layer module. After mounting of the individual detector elements to the substrate, electrical testing of the detector elements is hampered by the small size of the electrical contacts formed upon contemporary substrates, which makes probing difficult.
Furthermore, after mounting the substrate to the multi-layer module, faults which occur therein may only be detected via electrical testing through the circuitry of the multi-layer module, thus substantially limiting the type of testing which may be performed and also substantially increasing the complexity of such testing.
Indeed, it is difficult to troubleshoot problems which are found during such testing. For example, an indication of a high resistance connection between an individual infrared detector and its associated circuitry within the multi-layer module cannot easily be isolated to a particular electrical interconnection via such testing. It is not possible to determine whether the high resistance connection is at the interface of the substrate and the detector elements or, conversely, if at the interface of the substrate and the multi-layer module. Thus, electrical testing performed subsequent to attachment of the substrate to the multi-layer module tends to provide test results which are ambiguous and of only limited help in fault isolation.
As such, it is beneficial to provide a means for testing individual infrared detectors both prior to and after interconnection with the multi-layer module wherein accurate troubleshooting of the individual infrared detector elements, as well as their associated electrical interconnections, is similarly facilitated.
Handling and mounting of the infrared detector elements to a multi-layer module, even after attachment of the detector interface device or substrate thereto, is difficult. Handling of the infrared detector elements is difficult both due to the small size and delicate nature thereof. It is extremely difficult to grasp the infrared detector elements, even when mounted upon the substrate, in a manner which is both secure and which is not likely to cause damage thereto.
As such, it is additionally beneficial to provide a means for handling infrared detector elements and attaching the infrared elements to multi-layer modules in a manner which is reliable and which is not likely to cause damage thereto.